1. Field of the Invention
The present invention relates to byte code instrumentation and more particularly to resolving references to objects referenced by byte code instrumented logic.
2. Description of the Related Art
Byte code instrumentation relates to the augmentation of existing byte code in a compiled object to produce a modified version of the compiled object. Byte code instrumentation often arises where an existing application is to be configured for performance monitoring and performance profiling. Whereas in the past, the application could be modified directly through a modification of source code to produce the instrumented form of the application, this presupposes the availability of the source code for an application. Byte code instrumentation has become prevalent particularly in the circumstance where one cannot access the source code for an application. In the latter circumstance, the application itself must be modified in compiled form subsequent to the invocation of the application, but prior to the execution of the application.
When classes are added to target byte code, it often becomes the case that class references arising from the byte code instrumentation of the target byte code cannot be located at run-time. Generally, a class may not be located where the class has not been included from the class path. When encountering a missing class referenced by the augmented logic of the target byte code, a “No Class Definition Found” exception can arise and the augmentation will fail.
In the past at least two solutions have been proposed to address the possibility that a class reference in an augmented form of target byte code cannot be found. One solution dictates that the referenced classes are added to a folder already listed in the class path. To add a referenced class to a folder already listed in the class path, however, can require substantial end user interaction with the command line or process environment thus making the use of such a tool intrusive. Yet, it is desirable to strive for an appearance of seamlessness in the operation of instrumented byte code.
A second solution directs the addition of the referenced class to an extension folder. The second solution, like the first solution, is not without its flaws. Specifically, in the second solution, the end user again is required to intervene by copying files to a virtual machine installation location which may be difficult to determine and may not be modifiable by the user. Also, reinstalling or upgrading the virtual machine can result in the loss of the referenced class in the extension folder. In the presence of multiple, installed virtual machines, the problem can be compounded. Finally, where a custom class loader has supplanted the system class loader, the custom class loader may lack a configuration for locating the referenced classes in the extension folder.